Rickettsia

• What type of bacteria is Rickettsia?

  Gram negative obligate intracellular bacteria
• What is the size range of Rickettsia bacteria?

  0.3-0.5 x 0.8-1 µm
• What hosts are Rickettsia associated with?

  Arthropod or helminth hosts
• How many groups are pathogenic Rickettsia classified into?

  Three groups
• What are the three groups of pathogenic Rickettsia and their associated vectors?

  • Spotted fever group: tick-borne rickettsioses
  • Typhus group: body louse
  • Scrub typhus: chiggers
• Where do Rickettsia mainly inhabit in infected cells?


  In the cytosol of infected cells
• Why do Rickettsia depend on their environment?

  For the supply of many nutrients
• What critical enzymes do Rickettsia lack genes for?

  Several critical enzymes necessary for metabolism
• What are the diseases caused by different Rickettsia species and their primary vectors?

  • R. prowazekii: Epidemic typhus, transmitted by body louse
  • R. typhi: Murine typhus, transmitted by flea faeces
  • R. rickettsii: Rocky Mountain spotted fever, transmitted by tick bite
  • R. africae: African tick bite fever, transmitted by tick bite
  • R. felis: Flea borne spotted fever, transmitted by flea and undetermined mechanism
• What is the primary vector for R. prowazekii?

  Body louse
• What disease is caused by R. typhi?

  Murine typhus
• What is the primary vector for R. rickettsii?

  Tick
• Where is R. africae primarily distributed?

  Africa/West Indies
• How are Rickettsioses typically transmitted to humans?

  By arthropods such as ticks, mites, fleas, lice, or chiggers
• What determines the geographic distribution of Rickettsia?

  The distribution of the infected arthropod, which is the reservoir host
• What type of populations are affected by louse transmitted diseases?

  Poor people in cold places
• What is the role of tick behavior in Rickettsia transmission?

  Tick behavior determines the targeted population and seasonality
• What percentage of ticks carry any Rickettsia?

  Only 4%
• How are Rickettsia transmitted through ticks?

  Transstadially (stage by stage) and transovarially
• What leads to widespread microvascular injury in Rickettsial infections?

  Direct rickettsial injury and immunopathological mechanisms mediated via cytokines
• What are common clinical presentations of Rickettsial infections?

  Fever, myalgias, headaches, nausea, vomiting, and rash
• What is a late sign of Rickettsial infection involvement?


  Involvement of the palms and soles
• What laboratory methods are used for diagnosing Rickettsial infections?

  Serology (immunofluorescence) and PCR of blood or eschar swab
• What is the preferred method for demonstrating antibodies to Rickettsial antigens?

  The indirect fluorescence antibody test or latex agglutination
• What is the challenge in culturing Rickettsiae in the laboratory?

  They can only be cultivated in viable eukaryotic host cells
• What are the treatment options for Rickettsial infections?

  • Early treatment with doxycycline, tetracycline, or chloramphenicol is effective
  • Antibiotics have no effect on Rickettsiae in their natural ecological niches
  • No vaccines are currently available
• What are the control measures for preventing Rickettsial infections?

  • Control of vector and reservoir hosts
  • Massive delousing with insecticide can abort typhus fever epidemics
  • Prevention of tick attachment and removal before they inject Rickettsiae
  • Control of rodent populations to reduce exposure to R. typhi and R. akari